As an example of an antenna apparatus for use in a mobile radio communication apparatus, a whip antenna, which is used in a cellular phone, can be named.
As shown in FIG. 1, a cellular phone 2, which comprises a whip antenna 1, has an antenna configuration in which a call can be established even in a state that a whip antenna 1 is extended or contained.
In a case of a bad receiving and transmitting state, a user of cellular phone 2 extends whip antenna 1 from a main body of cellular phone 2 to improve the receiving and transmitting state, so that the user can make a call. Also, when the extended whip antenna 1 obstructs the carrying or the telephone call in a good receiving and transmitting state, the user of cellular phone 2 contains the whip antenna 1 in the main body, so that the user can make a call.
FIGS. 2A and 2B are cross-sectional views showing the configuration of the conventional whip antenna used in the cellular phone. FIG. 2A shows a state that the whip antenna is extended from the main body, and FIG. 2B shows a state that whip antenna is contained in the main body.
As shown in FIGS. 2A and 2B, the conventional whip antenna 1 is attached to a housing 11 of the cellular phone 2 with an attaching member 12. The whip antenna 1 has a configuration in which a screw antenna 13 and a mono-pole antenna 14 are combined. The screw antenna 13 and mono-pole antenna 14 are electrically insulated from each other by an insulating member 15 inserted between these antennas.
As shown in FIG. 2A, when the whip antenna 1 is extended, a radio circuit substrate 16 is electrically connected to a mono-pole antenna base portion 18 through a feeding spring 17. At this time, a portion from radio circuit substrate 16 to mono-pole antenna 14 is conductive, and only mono-pole antenna 14 is electrically powered and functions as an antenna.
While, as shown in FIG. 2B, when the whip antenna 1 is contained in a housing 11 down to a portion where a resin mold 19 for protecting screw antenna 13 comes in contact with attaching member 12, radio circuit substrate 16 is electrically connected to a screw antenna base portion 20 through feeding spring 17. At this time, a portion from radio circuit substrate 16 to screw antenna 13 is conductive, and only screw antenna 13 is electrically powered and functions as an antenna.
In such an antenna apparatus for use in a mobile radio communication apparatus, there is a problem in widening the receiving and transmitting band, particularly the widening of the band of screw antenna 13. More specifically, in the current digital system cellular system in Japan, the distance between the transmitting band and the receiving band is 112 MHz, and the band necessary for the entirety of system is 148 MHz.
The following can be considered as one of solutions to widen screw antenna 13. Namely, a coil diameter of screw antenna 13, the pitch, the number of turns are optimized. Moreover, as shown in FIG. 2, the screw antenna base portion 20 is divided into two and a spacer 21, made of a dielectric material, is inserted therebetween, so that an LC series resonance circuit is formed. This equalizes the impedance characteristic of screw antenna 13 with that of mono-pole antenna 14.
Since the impedance characteristic of screw antenna 13 is equivalent to that of mono-pole antenna 14, screw antenna 13 connected to the radio circuit substrate 16, which matches mono-pole antenna 14, can obtain the same wide band characteristic as mono-pole antenna 14.
However, in the conventional whip antenna 1, both faces of spacer 21 must be bonded with an adhesive, etc., and there is a problem in which mechanical strength of the bonded portion is insufficient to bending and tension of whip antenna 1.